Blood type is a classification of blood based on the presence or absence of inherited antigenic substances on the exterior surface of red blood cells. The A and B antigens have trisaccharide structures [A, GalNAcα1-3(Fucα1-2)Galβ1; and B, Galα1-3(Fucα1-2)Galβ1] attached to a variety of glycolipids and glycoproteins on the erythrocyte (red blood cell) surface. Group O individuals lack the terminal glycosyltransferases necessary to produce the A or B antigens and carry the disaccharide H antigen (Fucα1-2Galβ1).
Recent studies suggest that blood group antigen diversity may provide a mechanism of pathogen evasion whereby distinct ABO(H) antigen structures may reduce pathogen attachment and therefore infectivity. Because ABO(H) antigens are composed of carbohydrate structures that only differ by distinct monosaccharides on the terminal structures of glycans, factors that might be responsible for providing innate immunity toward pathogens expressing blood group antigens should recognize carbohydrates.
Bacteria generate a wide variety of glycan-based antigenic structures, many of which can possess blood group antigen activity. For example, E. coli O86 cross-reacts with antibodies specific for human blood group B and induces high titers of blood group B-specific antibodies in previously unexposed individuals. Notably, whereas individuals of blood group A or O produce antibodies that kill E. coli O86, individuals with blood group B do not generate antibodies capable of altering E. coli O86 viability, providing a specific example of the immunological limitation in adaptive immunity toward a blood group antigen-bearing pathogen. Springer & Horton, J. Clin. Invest. 48, 1280-1291 (1969) and see also Vasta, Nat. Rev. Microbiol. 7, 424-438 (2009) entitled “Roles of galectins in infection.”